Many pharmaceuticals are derived from plants and indeed many plants or extracts obtained therefrom are taken as medicines. There are over 120 distinct chemical substances derived from plants that are considered as important drugs that are currently in use. The table below lists some of these substances.
There are many examples of plant-based substances that are known for their medicinal properties. For example a tropical plant, Cephaelis ipecacuanha, is known to produce the chemical emetine. A drug was developed from this substance called Ipecac; this was used for many years to induce vomiting. Another example of plant-based substances used as medicines is the plant chemical named taxol found in the Pacific Yew tree. The taxol molecule was produced synthetically to produce the drug PACLITAXEL™, which is used in the treatment of various types of tumours.
The plant substance, cynarin, is a plant chemical found in the common artichoke (Cynara scolymus). A cynarin drug is sold for the treatment of liver problems and hypertension. The drug is simply an extract from the artichoke plant that has been standardized to contain a specific amount of cyanarin. Similarly the substance silymarin is a chemical found in the milk thistle plant and natural milk thistle extracts that have been standardized to contain specific amounts of silymarin are also used for the treatment of liver problems.
Some of the drugs/chemicals shown in the table below are sold as plant based drugs produced from processing the plant material. Many plant chemicals cannot be completely synthesised in the laboratory due to the complex nature of the plant extract. For example the tree Cinchona ledgeriana produces the substance quinine, which is used in to treat and prevent malaria. Quinine is now chemically synthesised; however, another chemical in the tree called quinidine, which was found to be useful for the treatment of heart conditions, couldn't be completely copied in the laboratory. The tree bark is used to produce a quinidine extract.
The table below details some of the plant-based medicines that are in use today.
Drug/ChemicalAction/Clinical UsePlant SourceAcetyldigoxinCardiotonicDigitalis lanataAdonisideCardiotonicAdonis vernalisAescinAnti-inflammatoryAesculus hippocastanumAesculetinAnti-dysenteryFrazinus rhychophyllaAgrimopholAnthelminticAgrimonia supatoriaAjmalicineCirculatory DisordersRauvolfia sepentinaAllantoinWound healingSeveral plantsAllyl isothiocyanateRubefacientBrassica nigraAnabesineSkeletal muscle relaxantAnabasis sphyllaAndrographolideBaccillary dysenteryAndrographis paniculataAnisodamineAnticholinergicAnisodus tanguticusAnisodineAnticholinergicAnisodus tanguticusArecolineAnthelminticAreca catechuAsiaticosideWound healingCentella asiaticaAtropineAnticholinergicAtropa belladonnaBenzyl benzoateScabicideSeveral plantsBerberineBacillary dysenteryBerberis vulgarisBergeninAntitussiveArdisia japonicaBetulinic acidAnticancerousBetula albaBorneolAntipyretic, analgesic,Several plantsanti-inflammatoryBromelainAnti-inflammatory,Ananas comosusproteolyticCaffeineCNS stimulantCamellia sinensisCamphorRubefacientCinnamomum camphoraCamptothecinAnticancerousCamptotheca acuminata(+)-CatechinHaemostaticPotentilla fragarioidesChymopapainProteolytic, mucolyticCarica papayaCissampelineSkeletal muscle relaxantCissampelos pareiraCocaineLocal anaestheticErythroxylum cocaCodeineAnalgesic, antitussivePapaver somniferumColchiceine amideAnti-tumour agentColchicum autumnaleColchicineAnti-tumour agent,Colchicum autumnaleanti-goutConvallatoxinCardiotonicConvallaria majalisCurcuminCholereticCurcuma longaCynarinCholereticCynara scolymusDanthronLaxativeCassia speciesDemecolcineAnti-tumour agentColchicum autumnaleDeserpidineAntihypertensive,Rauvolfia canescenstranquillizerDeslanosideCardiotonicDigitalis lanataL-DopaAnti-parkinsonismMucuna speciesDigitalinCardiotonicDigitalis purpureaDigitoxinCardiotonicDigitalis purpureaDigoxinCardiotonicDigitalis purpureaEmetineAmoebicide, emeticCephaelis ipecacuanhaEphedrineSympathomimetic,Ephedra sinicaantihistamineEtoposideAnti-tumour agentPodophyllum peltatumGalanthamineCholinesterase inhibitorLycoris squamigeraGitalinCardiotonicDigitalis purpureaGlaucarubinAmoebicideSimarouba glaucaGlaucineAntitussiveGlaucium flavumGlasiovineAntidepressantOctea glazioviiGlycyrrhizinSweetener, Addison'sGlycyrrhiza glabradiseaseGossypolMale contraceptiveGossypium speciesHemsleyadinBacillary dysenteryHemsleya amabilisHesperidinCapillary fragilityCitrus speciesHydrastineHemostatic, astringentHydrastis canadensisHyoscyamineAnticholinergicHyoscyamus nigerIrinotecanAnticancer, anti-tumourCamptotheca acuminataagentKaibic acudAscaricideDigenea simplexKawainTranquillizerPiper methysticumKheltinBronchodilatorAmmi visagaLanatosides A, B, CCardiotonicDigitalis lanataLapacholAnticancer, anti-tumourTabebuia speciesa-LobelineSmoking deterrant,Lobelia inflatarespiratory stimulantMentholRubefacientMentha speciesMethyl salicylateRubefacientGaultheria procumbensMonocrotalineAnti-tumour agentCrotalaria sessiliflora(topical)MorphineAnalgesicPapaver somniferumNeoandrographolideDysenteryAndrographis paniculataNicotineInsecticideNicotiana tabacumNordihydro-AntioxidantLarrea divaricataguaiaretic acidNoscapineAntitussivePapaver somniferumOuabainCardiotonicStrophanthus gratusPachycarpineOxytocicSophora pschycarpaPalmatineAntipyretic, detoxicantCoptis japonicaPapainProteolytic, mucolyticCarica papayaPapavarineSmooth muscle relaxantPapaver somniferumPhyllodulcinSweetnerHydrangea macrophyllaPhysostigmineCholinesterase InhibitorPhysostigma venenosumPicrotoxinAnalepticAnamirta cocculusPilocarpineParasympathomimeticPilocarpus jaborandiPinitolExpectorantSeveral plantsPodophyllotoxinAnti-tumour, anticancerPodophyllum peltatumagentProtoveratrines A, BAntihypertensiveVeratrum albumPseudoephredrine*SympathomimeticEphedra sinicaPseudoephedrine,SympathomimeticEphedra sinicanor-QuinidineAntiarrhythmicCinchona ledgerianaQuinineAntimalarial, antipyreticCinchona ledgerianaQuisqualic acidAnthelminticQuisqualis indicaRescinnamineAntihypertensive,Rauvolfia serpentinatranquillizerReserpineAntihypertensive,Rauvolfia serpentinatranquillizerRhomitoxinAntihypertensive,Rhododendron molletranquillizerRorifoneAntitussiveRorippa indicaRotenonePiscicide, InsecticideLonchocarpus nicouRotundineAnalgesic, sedative,Stephania sinicatranquilizerRutinCapillary fragilityCitrus speciesSalicinAnalgesicSalix albaSanguinarineDental plaque inhibitorSanguinaria canadensisSantoninAscaricideArtemisia maritmaScillarin ACardiotonicUrginea maritimaScopolamineSedativeDatura speciesSennosides A, BLaxativeCassia speciesSilymarinAntihepatotoxicSilybum marianumSparteineOxytocicCytisus scopariusSteviosideSweetenerStevia rebaudianaStrychnineCNS stimulantStrychnos nux-vomicaTAXOL ®Anti-tumour agentTaxus brevifoliaTeniposideAnti-tumour agentPodophyllum peltatumTetra-Antiemetic, decreaseCannabis sativahydrocannabinolocular tensionTetrahydropalmatineAnalgesic, sedative,Corydalis ambiguatranquilizerTetrandrineAntihypertensiveStephania tetrandraTheobromineDiuretic, vasodilatorTheobroma cacaoTheophyllineDiuretic, bronchodilatorTheobroma cacao andothersThymolAntifungal (topical)Thymus vulgarisTopotecanAnti-tumour, anticancerCamptotheca acuminataagentTrichosanthinAbortifacientTrichosanthes kirilowiiTubocurarineSkeletal muscle relaxantChondodendrontomentosumValapotriatesSedativeValeriana officinalisVasicineCerebral stimulantVinca minorVinblastineAnti-tumour,Catharanthus roseusAntileukemic agentVincristineAnti-tumour,Catharanthus roseusAntileukemic agentYohimbineAphrodisiacPausinystalia yohimbeYuanhuacineAbortifacientDaphne genkwaYuanhuadineAbortifacientDaphne genkwa
There are many examples of extracts that are characterized by reference to a supposed active or marker. The principle described herein with reference to cannabis plants would thus be applicable to other plant types as are shown in the table above.
As an example of a botanical drug, Cannabis sativa has been used as a drug for centuries, although the precise basis for the plants activity is not known. Both THC and CBD, two of the plants cannabinoids, are known to have distinct pharmacological activities and Marinol® (THC) and Sativex® (an extract containing defined amounts of both THC and CBD) are approved products for various medical indications.
In the case of extracts it is of course unclear whether the efficacy of a botanical drug extract is attributable to the identified “active(s)” or “markers” and/or other components present in an extract which may provide an unidentified additive or synergistic effect or in fact be directly responsible for the activity.
In the case of cannabis the supposed actives, the cannabinoids, are produced through a series of enzymatic synthesis which are outlined below:
The first specific step in the pentyl cannabinoid biosynthesis is the condensation of a terpenoid moiety, geranylpyrophosphate (GPP), with the phenolic moiety, olivetolic acid (OA; 5-pentyl resorcinolic acid), to form cannabigerol (CBG). This reaction is catalysed by the enzyme geranylpyrophosphate:olivetolate geranyltransferase (GOT); [1]. Precursors for GPP are the C5 isomers isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). These compounds can originate from two different pathways:                the mevalonate pathway (MVA) that is located in the cytoplasm; and        the deoxyxylulose pathway (DOX) that operates in the plastid compartments.        
According to Fellermeier et al. [2], the GPP incorporated into cannabinoids is derived predominantly, and probably entirely, via the DOX pathway of the glandular trichome plastids. The phenolic moiety OA is generated by a polyketide-type mechanism. Rahaijo et al. [3] suggest that n-hexanoyl-CoA and three molecules of malonyl-CoA condense to a C12 polyketide, which is subsequently converted into OA by a polyketide synthase.
CBG is the direct precursor for each of the compounds THC [4], CBD [5] and CBC [6], [7] and [8]. The different conversions of CBG are enzymatically catalysed, and for each reaction an enzyme has been identified: THC acid synthase [4] CBD acid synthase [5] and CBC acid synthase [7] and [8].
Cannabinoids with propyl side chains, as identified by Vree et al. [9] and de Zeeuw et al. [10], result if GPP condenses with divarinic acid (DA; 5-propyl resorcinolic acid) instead of OA, into cannabigerovarin (CBGV). The condensation of n-hexanoyl-CoA and two, instead of three, molecules of malonyl-CoA, results in a C10 polyketide, which is subsequently cyclisised into DA by a polyketide [11]. The three cannabinoid synthase enzymes are not selective for the length of the alkyl side chain and convert CBGV into the propyl homologues of CBD, THC and CBC, which are indicated as cannabidivarin (CBDV), delta 9-tetrahydrocannabivarin (THCV) and cannabichromevarin (CBCV), respectively [12].